Smoker's Lung: Pathology Photo Essay (cont.)

Michael C. Fishbein, MD

Dr. Fishbein received his undergraduate and medical degrees from the University of Illinois. He completed a residency in anatomic and clinical pathology at Harbor General Hospital/UCLA Medical Center. He is board certified in anatomic and clinical pathology.

Jay W. Marks, MD

Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

What processes determine normal function of the lung?

As just indicated, the main function of the lung is the exchange of the gases oxygen and carbon dioxide. So, the blood in the alveolar capillaries takes oxygen from inhaled air that is in the alveoli. Then, the oxygenated blood circulates through the body to deliver the oxygen to the tissues. In the exchange of gases, the blood in the alveolar capillaries releases carbon dioxide to the alveoli. Then, when we breathe out (exhale or expire), the carbon dioxide is removed from the alveoli through the airway and eliminated from body. Accordingly, three processes determine normal lung function:

Ventilation

Diffusion

Blood supply

Ventilation is the moving of air into and out of the lung. This process requires an open (unobstructed) airway. Increasing and decreasing the size of the chest cavity is what accomplishes the movement of air. You see, as the chest cavity enlarges, a vacuum is created in the airway and air rushes in. Then, with breathing out, the chest cavity becomes smaller and air is pushed out. The muscles in the chest wall (intercostal muscles between the ribs), and the muscles in the diaphragm work together to change the size of the chest cavity. (The diaphragm is a flat muscular membrane that separates the chest from the abdomen.) In addition, when we breathe really hard, we even use muscles in the neck (referred to as accessory muscles for breathing) to help expand the chest.

Diffusion is the process that accomplishes the actual gas exchange across the alveolar walls. This process requires normal alveolar septae (the walls of the air sacs) that contain intact capillaries. Finally, a normal blood supply depends on normal capillaries, normal red blood cell counts (no anemia), and normal pumping of blood by the heart. Any disease that interferes with ventilation, diffusion, or blood supply to the lung will impair lung (pulmonary) function and decrease delivery of oxygen to the tissues of the body.